The present invention relates a novel chlorofluorohydrocarbon and to a novel process for its preparation. More particularly it relates to 1,1-difluoro-1,4-dichlorobutane and processes for preparing it from the known compounds 1,1,1,4-tetrachlorobutane and 1,1,4-trichlorobut-1-ene.
Accordingly the present invention provides 1,1-difluoro-1,4-dichlorobutane.
In a further aspect the present invention provides a process for preparing 1,1-difluoro-1,4-dichlorobutane comprising reacting 1,1,1,4-tetrachlorobutane or 1,1,4-trichlorobut-1-ene with hydrogen fluoride in the liquid or vapour phase.
The process of the present invention is illustrated using 1,1,1,4-tetrafluorobutane as starting material by the following reaction scheme: 
The reaction is conveniently conducted in a vessel whose lining is resistant to corrosion by chemical reaction with hydrogen fluoride, such as for example, one made from xe2x80x9cHastalloyxe2x80x9d (Registered Trade Mark) or Monel metal. When the reaction is conducted in the vapour phase it is conveniently conducted by passing a stream comprising a mixture of the reactants through a heated reaction zone, preferably defined by a tubular vessel.
The reaction can conveniently be carried out in the presence of a catalyst such as a polyvalent metal halide or aluminium oxide.
Examples of suitable catalysts for liquid phase reactions include titanium halides, ferric chloride, particularly in the presence of activated charcoal, aluminium fluoride, aluminium oxide (xcex3-alumina), chromium fluoride, manganese difluoride, ferric fluoride, cobalt dichloride, nickel difluoride, zirconium fluoride, thorium fluoride, boron trifluoride, tantalum trifluoride, oxyfluorides and antimony pentachloride, particularly in the presence of activated charcoal.
Titanium halides which are suitable for use in liquid phase reactions include titanium chlorides, titanium fluorides and titanium bromides, particularly titanium (VI) chloride.
Tin halides are preferred catalysts for liquid phase reactions and a particularly useful catalyst is tin (IV) chloride.
Examples of suitable catalysts for vapour phase reactions include halides of aluminium, iron, chromium, vanadium, tungsten, tantalum, antimony, titanium, tin, zirconium, nickel, niobium, molybdenum, manganese, cobalt, thorium and mercury. Examples of specific catalysts include ferric chloride, particularly in the presence of activated charcoal, aluminium fluoride, aluminium oxide (xcex-alumina), chromium halides such as chromium chloride and chromium fluoride, manganese difluoride, ferric fluoride, cobalt dichloride, nickel difluoride, zirconium fluoride, thorium fluoride, oxyfluorides and antimony pentachloride, particularly in the presence of activated charcoal.
Chromium halides are preferred catalysts for vapour phase reactions and a particularly useful catalyst is chromium (III) chloride. The catalyst may be supported on alumina, which has preferably been pre-treated with a fluorinating agent such as sulfur tetrafluoride, so as to convert it, at least in part, to aluminium trifluoride.
For liquid phase reactions the reaction temperature is preferably in the range 50 to 150xc2x0 C., and more preferably in the range 70 to 90xc2x0 C. The duration of the reaction is usually in the range 4 to 10 hours.
For vapour phase reactions the reaction temperature is preferably in the range 100 to 400xc2x0 C., and more preferably in the range 135 to 250xc2x0 C. The reaction may be conducted under atmospheric pressure or at a pressure above atmospheric pressure, provided that the combination of pressure and temperature is chosen so as to ensure that the reactants and products remain in the vapour phase. The conversion rate is also dependent on various factors such as the residence time in the reaction zone, the ratios of the reactants and the concentration of the reactants as well as the presence of other components of the vapour stream. Preferably the stream contains an inert gaseous diluent to moderate the reaction, nitrogen is suitable for this purpose. The reactants and other components of the vapour stream should be free of any water.
The reaction is carried out using hydrogen fluoride which is a volatile material having a boiling point under normal atmospheric pressure of 19.5xc2x0 C; In order to conduct the reaction in the liquid phase a sealed reaction vessel may be used in which the reaction proceeds under the autogenic pressure of the reactants and products. In a preferred variant of the liquid phase process a vessel can be used which is equipped with means to permit the hydrogen chloride produced during the reaction to be vented, preferably continuously, whilst the reaction is maintained in the liquid phase by the autogenic pressure of the reactants and products. This may be achieved by the use of a condenser which liquefies evaporating hydrogen fluoride whilst permitting the escape of the more volatile hydrogen chloride gas. Such an arrangement permits the autogenic pressure to be maintained in the range of about 175 to about 500 psi, e.g. about 175 to about 230 psi.
The vapour phase reaction is preferably carried out by passing a gaseous mixture of hydrogen fluoride together with 1,1,1,4-tetrachlorobutane or 1,1,4-trichlorobut-1-ene at an elevated temperature diluted with nitrogen through a reaction zone defined by a metal tube heated to a temperature in the range 130 to 250xc2x0 C., and thereafter cooling the reactant stream so as to condense out the mixture of reactants and products, which can then be separated by fractional distillation. In a preferred variant of the vapour phase process a receiving vessel can be used which is equipped with means to permit the hydrogen chloride produced during the reaction to be vented, preferably continuously. This may be achieved by the use of a condenser which liquefies the hydrogen fluoride and the other less volatile components whilst permitting the escape of the more volatile hydrogen chloride gas.
The product mixture consists principally of the desired 1,1-difluoro-1,4-dichlorobutane, with minor quantities of other materials present including unreacted starting material and intermediate species formed during the process, for example 1,1,1-trifluoro-4-chlorobutane. When the reaction is conducted in the liquid phase at a temperature of 85 to 90xc2x0 C. with venting of the hydrogen chloride over a 6 to 7 hour period good yields and conversion rates may be obtained with minimal co-production of 1,1,1-trifluoro-4-chlorobutane. Isolation of the desired product can readily be achieved by fractional distillation and the unreacted starting material and intermediate species recycled back into the reactant stream. One such intermediate species formed during the process when 1,1,1,4-tetrachlorobutane is used as starting material is 1,1,4-trichlorobut-1-ene.
1,1-Difluoro-1,4-dichlorobutane is a novel compound which has useful properties as a solvent, and may be used, for example, in degreasing electrical and electronic components such as printed circuits and the like. Because of its higher boiling point and lower volatility compared with the halomethanes and haloethanes traditionally used for degreasing, and the fact that it is a chlorofluorohydrocarbon and not a chlorofluorocarbon, its use may have environmental advantages. It is also of use as a synthetic chemical intermediate particularly for introducing fluorocarbon functionality into a molecule, for example as a means of introducing the difluorobutenyl group into the nematicidal compounds of International Patent Applications WO 94/06777 and WO 95/24403.
Various further preferred features and embodiments of the present invention will now be described with reference to the following non-limiting examples, in which Examples 1 to 7 relate to liquid phase reactions and Examples 8 to 10 relate to vapour phase reactions. It will be understood that whereas the Examples disclose experimental procedures which show that the process of the invention can be used to produce the desired product, they may not necessarily disclose the most advantageous conditions for ensuring the economically optimal production of the desired product. Such conditions would be established by a process of routine examination of variation of the conditions within the alternatives and ranges set out herein and any such optimised process may be considered as being included within the scope of the invention.